Color is the property of reflecting light of a particular visible wavelength. Duplication of color of pigments and paints therefore requires attention to the influence of the light source in which the "match" (or lack of it) will be viewed. One of the most unforgiving light sources, for proving or disproving a color match, is "noon daylight," in which paints or pigments which appear the same or very similar under other light sources can take on very different aspects of color.
To attempt to meet the various needs of a variety of industries and applications for which color matching is required, numerous artificial lights have been developed. These lights have approximated daylight to an extent, with varying degrees of success. U.S. Pat. No. 1,249,443 (1917) discloses "corrected" artificial light equivalent to daylight as a part of the claimed device. No specifics elucidate the correction of artificial light in this way, however. U.S. Pat. No. 1,330,028 discloses a "standard light of a given spectral composition, for the purpose of matching colors . . . ," accomplished with a lamp combined with reflectors and deflectors. U.S. Pat. No. 3,093,319 discloses an illuminating device having a plurality of fluorescent and incandescent bulbs, together, which in combination can provide either a progressive range of lighting or a certain number of preselected combinations from the light sources. Fluorescent dustings and filters are disclosed as modifiers for the radiation spectrum emitted by the light sources.
U.S. Pat. No. 3,112,886 explains that "a fixture manufacturer cannot purchase a light source such as a fluorescent tube capable of giving off illumination which is color corrected to standard sun illumination." To address this problem, the fixture includes a reflector, for a standard warm white fluorescent lamp, which is coated with specially selected colored particles or beads.
U.S. Pat. No. 4,651,259 discloses a light reflector comprised of a plurality of elongate prismatic bodies rotating about their longitudinal axis. U.S. Pat. Nos. 3,588,488 and 4,072,856 disclose high-Kelvin light fixtures for medical, dental and surgical applications. U.S. Pat. No. 4,091,441 discloses a fixture containing two types of fluorescent lamps.
Finally, one patent, U.S. Pat. No. 3,201,576 to Scott, contains extensive text pertaining to various approximations of artificial daylight. According to Scott, "daylight" fluorescent tubes, even though whitish, do not duplicate the spectral energy distribution curve for north sky daylight. Combined sources of light did not necessarily overcome the unwanted "blue shift" of daylight bulbs, and included among the disclosed disadvantageous arrangements are fixtures containing both fluorescent and incandescent lights, due to their overheating problems and the relatively lower ratio of lumens output/watts input. Scott discloses and claims an all-fluorescent fixture.
Although pursuit of artificial daylight has a long tradition, success (or lack of it) is exposed by the chromaticity meter, known in the art. When the same color test panel is subjected to "natural daylight" and so-called "artificial daylight," alternately, and separate chromaticity readings are taken under each circumstance, the chromaticity meter readings provide objective evidence of the efficacy with which the artificial daylight has simulated the natural daylight. Those skilled in the art are aware that prior art artificial daylight devices eventuate significantly different chromaticity readings from natural light, when a single color swatch is tested alternately. Therefore, a need remains for a method and apparatus which can illuminate a color test panel and provide a chromaticity meter reading insignificantly different from the chromaticity meter reading of the same color test panel in natural daylight.